Conventional hand cleansing formulations contain solvents and/or surfactants capable of solubilizing or emulsifying soils present on the skin's surface. The cleaning products may come in the form of, for instance, a bar soap which produces a lather or foam by agitation with the hands in the presence of water or a gel that may be, for instance, pumped from a dispenser.
Recently, consumer foamable cleansers have appeared on the market. Foamable cleansers are typically kept in a dispensing container that mixes the cleansing composition with air when dispensed immediately forming a foam or lather. These types of products have been used extensively in the medical field by doctors and other medical personnel. Compositions dispensed as foams have been regarded as desirable in part because of an association of foam with cleaning ability.
The liquid-gas foams are composed of gas cells surrounded by a liquid. The gas cells consist of films of liquid (lamellae) surrounding the gas bubble with the planar faces of liquid films meeting at angular intersections called Plateau junctions. To be mechanically stable, the lamellae of three bubbles meeting must be at an angle of 120°. With the addition of more bubbles to the foam, the perfect angle for mechanical stability is lost and the bubbles take on a more polygonal type of network. In a three dimensional gas cell within a foam, the resulting cell is polyhedral in nature.
A liquid-gas foam can be considered an emulsion with the liquid being the continuous phase and the dispersed phase composed of gas bubbles. Surfactants are frequently used to form most foams. The surfactants reduce the surface tension of the liquid phase and stabilize the films against rupture. The polar heads of the surfactants arrange themselves within the polar liquid and the hydrophobic tails project out into the air if the bubble is on the outside of the film, or into the Plateau junction if the bubble is within the film.
Liquid-gas foams can be categorized into dry and wet foams. In a dry foam, there is very little liquid (less than 1% by volume) and it exists in very thin films. The junctions of these films can be visualized in terms of a thin line with no discernable width. The polyhedral nature of the gas cell is clearly visible and very little fluid is maintained within the foam making this foam fairly stable.
A foam containing a percent or more of liquid is considered a wet foam. Liquid accumulates in the Plateau borders of these foams causing them to increase in width. Due to the swelling of the Plateau junctions, the corners and edges of the polyhedral cell are rounded off. Pressure differences between adjacent cells and gravity force liquid from these foams passing the liquid through the Plateau junctions (drainage) to the substrate until the lower-energy dry foam is reached or the bubble ruptures. However, with increased liquid, the cells regain their spherical nature and the foam degrades into a bubbly liquid.
For a liquid to foam with any degree of success, it must be able to expand its surface area to form a membrane around gas bubbles, possess the correct rheological and surface properties to reduce the thinning of the lamellae leading to bubble coalescence, and slow the diffusion of gas across lamellae from small to large bubbles or to the surrounding atmosphere.
One problem that has been experienced in the past in formulating foamable cleansers is the ability to incorporate an alcohol into the compositions. Alcohols, for instance, have very effective sanitizing properties. Alcohols, however, are also known defoaming agents making their incorporation into foamable cleansers somewhat problematic. For example, alcohols reduce the surface tension of water in surfactant/water solutions below that needed to maintain the integrity of the lamellae of the foam bubble. Alcohols also displace surfactant molecules at the air/water interface disrupting the stabilization of any foam being formed and causing collapse.
As a consequence, in the past, foamable hand sanitizers containing alcohols have been placed in aerosol containers that produce a pressure high enough to generate a foam. Alternatively, alcohols have been combined with expensive or complicated ingredients in order to facilitate formation of a foam. For instance, those skilled in the art have proposed in the past adding fluorinated surfactants, such as a perfluoroalkylethyl phosphate, to sanitizing compositions containing alcohol.
In view of the above, a need currently exists for an improved foamable cleansing composition that contains a sanitizer. In particular, a need exists for a foamable sanitizing composition that contains an alcohol sanitizer.